Topic: Bigger wheel size, yes or no

2001 VW golf, I'm running 15 inch wheels now but have been thinking of running 17s , good or bad idea ? Thanks in advance to all your professional opinions.

2 (edited by mobius911 2018-10-20 05:25 PM)

Re: Bigger wheel size, yes or no

Is this being done for better lap times or better tire availability?

The 17s will increase weight (rotational mass) and result in taller effective gearing. Probably not the best idea for a low horsepower car.

Re: Bigger wheel size, yes or no

I'm looking for better lap times and room for bigger brakes

Re: Bigger wheel size, yes or no

We started our 91 accord on 17x8s with 225 45 17s.   The bolt pattern was right so one day I put them on my honda fit and drove it around for a few days.  I thought it would be fun to have 200tw tires on my daily driver for a bit.  It was terrible, like I had several hundred pounds of scrap steel  in the trunk.  I couldn't believe how much power those huge wheels and tires ate up.   So we went out and found to some 16x7 wheels with I think 205 40 16s for the race car.  It was amazing how much quicker this seemed on our Accord.  Cars that I used to have to race with for a few laps before getting around were now easy to pass.  We still are not going win anything but it sure makes it more fun while we are out there.  Bigger ain't always better.  Rotational and unsprung weight matter so does final drive ratio.

Re: Bigger wheel size, yes or no

leondetweiler wrote:

I'm looking for better lap times and room for bigger brakes

The former is almost always a function of better driving/traffic management, then suspension, then brakes, then power.  Keep that in mind when wanting faster lap times.  If you have max'ed out your skills, get it to turn better.  Of course this goes out the window if you are talking "fastest lap" but many successful teams in B and C only use that to indicate when a driver needs to be told to slow down and stop overdriving the car.

Winning weekends are more about reliability, staying out of the penalty box, pit efficiency/speed, and stint length.

The tire availability and bigger brakes are important things.  That said, every VW team I have met loses time in the pits changing wheel bearings (not every reace but often) until they figure out the secret sauce.  Taller, heavier wheels might contribute to early failure especially if you go wider and can exploit a better sorted suspension by increaing those cornering forces to levels 2-3 times higher than the factory ever planned.

6 (edited by jrbe 2018-10-21 04:59 AM)

Re: Bigger wheel size, yes or no

As mentioned the 2" larger wheels will slow you down. If you're melting down brakes and tried everything, going to a larger wheel is the right choice. Go only as big as you have to.
We went from 15" to 17". Under the 15's we melted down the biggest oe upgrade brakes we could fit, then largest Wilwood 4 piston setup we could fit with Hawk hp-10 pads in under 2 hours of on track time.
We ended up doing 6 piston touareg calipers w/ 330mm rotors. They were good for the first day and a half but the carbotec pads had horribly uneven deposits by the 2nd day. I thought it was going to rip the front suspension apart. The car was noticeably slower with the change but the brakes were there for us the whole race. That peace of mind was worth the loss of acceleration for us.
We also did a 5 lug swap to make this happen (and to get larger wheel bearings in there.) That forced us rwd for a race (had to mod front axles to work with new front components and didn't have time.) We have that sorted now (awd back) and working on some other upgrades this winter. It was a slippery slope for us.

-Killer B's (as in rally) '84 4000Q 4.2V8. Audis never win?

Re: Bigger wheel size, yes or no

Just to clarify a few things here:

Larger diameter wheels will not improve performance inherently. They will increase rotational mass, which I've always used a rule of thumb of rotational mass being worth 3x normal mass as you have to accelerate it up to much high rotational speeds than the linear speed of the car. Keep in mind that this can be mitigated if you're going from small heavy steelies to bigger but lighter alloys or racing oriented wheels.

As far as final gearing, this comes down to the tire outer diameter, so bigger wheels doesn't necessarily effect this. However, unless you use smaller profile wheels, you will see a taller final drive ratio. Don't assume this is bad though. All it really does is move your power band in relation to vehicle speed. Depending on where you are in the RPM range coming out of corners, this might actually help. Of course, you would still have to overcome the aforementioned increase in rotational mass.

Wider tires *can* improve handling. Bigger wheels often allow wider tires which affords you a larger contact patch which can help improve the available grip. However, if you do not have a suspension setup that is adjusted to utilize this properly, you won't see any gains here. However, regardless of how well tuned your suspension is, you are very likely to drastically increase the load on your wheel bearings if you have to space out the wheels to fit bigger tires. Also, once more, wider tires are more rotational mass. Not only are they simply more rubber, but wider tires means all that extra mass is at the furthest point from the rotational center of the wheel making it that much heavier.

Re: Bigger wheel size, yes or no

Something that hasn't been mentioned is the price difference between 15" tires and 17" tires is substantial.  Since we buy 6 new tires for each race, that adds up quick.

Also keep in mind that going with bigger wheels in order to fit bigger brakes likely won't help you stop any quicker.  Brakes don't stop the car, the tires do, and being we're all limited to street tires, the brakes can only do so much.

We run 15" wheels on our Integra, OE Honda brake calipers,  slighter larger rotors, and ST-43 pads.  No issues with braking, and the ST-43 pads will last at least three entire races.

Captain
Team Super Westerfield Bros.
'93 Acura Integra - No VTEC Yo!

Re: Bigger wheel size, yes or no

Brakes and tires work together to stop the car. Put 3x the power your car came with in and see how your brakes do on track.
Larger brakes have more heat capacity and can make much more braking power. The weak link is the weak link, not the whole chain.

There was a funny top gear episode about making a car faster around the track. Just about everything they did slowed their lap times. Big wheels and big brakes were 2 of their mods.

-Killer B's (as in rally) '84 4000Q 4.2V8. Audis never win?

Re: Bigger wheel size, yes or no

jrbe wrote:

Brakes and tires work together to stop the car. Put 3x the power your car came with in and see how your brakes do on track.
Larger brakes have more heat capacity and can make much more braking power.

Once the caliper is capable of locking the wheel, it can do no more.  True, larger brakes dissipate heat, which will make the brakes last longer without fade, but the tire's friction against the road is what really affects overall braking distance.  If your stock braking system can lock your wheels, a system with twice the size rotors and calipers will just lock the wheels more easily. IOW, you will stop quicker (shorter) on a DOT slick, vs. a 400 TWR tire using the same braking system.

The only reason we upgraded to slightly larger calipers (same piston size, larger pad surface) and rotors, was to gain longevity in the system, not to improve braking ability by reducing stopping distance.

YMMV.

Captain
Team Super Westerfield Bros.
'93 Acura Integra - No VTEC Yo!

Re: Bigger wheel size, yes or no

Another thing to consider with wheel selection it brake cooling.  Aluminum wheels will do a better job of transferring heat away from the brakes.  Larger wheels may also allow for better cooling since more air can get to the brakes.

Re: Bigger wheel size, yes or no

Run 225/50r16 and run GLI/20TH 312mm brakes with hawk blue pads.  In Lemons this setup worked great on 2002 gti  we just upgraded to ap racing 4 pistons as we were flexing calipers when the car got faster for a Higher series.

959 Toyota Tercel   6x Lemons loser

New England Area roll cages send me an email I'm in Central MA

Re: Bigger wheel size, yes or no

if you are killing pads that fast you might want to modify your driving habits we get 2 full races out ht10 pads withought a problem. same ish size pads as your golf. little heavier car.  more tire = more corner speed = less need for brakes.

Owner/Captain of The 27 Club E46. Phoenix, AZ
and now the #95 Thunderbird

Re: Bigger wheel size, yes or no

We run 15” tires, stock brakes on our E30.  17” wheels cost more and weigh more.  17” tires cost more and weigh more.

We have 3 sets of 15x8” rims that are waaaay cheaper than trying to find twelve 17” rims that will fit.

Agree on driving>>>>stint length>pit stop efficiency>tire width>horsepower>brake size in importance of winning races or doing well in any class.

LemonAid - Changing kids lives one lap at a time.

Re: Bigger wheel size, yes or no

No!

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